const win = window;
const lib = window['lib'] || (window['lib'] = {});
var doc = win.document;
var docEl = doc.documentElement;
var metaEl = doc.querySelector('meta[name="viewport"]');
var flexibleEl = doc.querySelector('meta[name="flexible"]');
var dpr = 0;
var scale = 0;
var tid;
var flexible = lib.flexible || (lib.flexible = {});

if (metaEl) {
  console.warn('将根据已有的meta标签来设置缩放比例');
  var match = metaEl.getAttribute('content').match(/initial\-scale=([\d\.]+)/);
  if (match) {
    scale = parseFloat(match[1]);
    dpr = parseInt(1 / scale);
  }
} else if (flexibleEl) {
  var content = flexibleEl.getAttribute('content');
  if (content) {
    var initialDpr = content.match(/initial\-dpr=([\d\.]+)/);
    var maximumDpr = content.match(/maximum\-dpr=([\d\.]+)/);
    if (initialDpr) {
      dpr = parseFloat(initialDpr[1]);
      scale = parseFloat((1 / dpr).toFixed(2));
    }
    if (maximumDpr) {
      dpr = parseFloat(maximumDpr[1]);
      scale = parseFloat((1 / dpr).toFixed(2));
    }
  }
}

if (!dpr && !scale) {
  var isAndroid = win.navigator.appVersion.match(/android/gi);
  var isChrome = win.chrome;
  var isIPhone = win.navigator.appVersion.match(/iphone/gi);
  var devicePixelRatio = win.devicePixelRatio;
  var isX5 = /TBS\/\d+/.test(win.navigator.userAgent);
  if (isIPhone || isChrome || isX5) {
    // iOS下，对于2和3的屏，用2倍的方案，其余的用1倍方案
    if (devicePixelRatio >= 3 && (!dpr || dpr >= 3)) {
      dpr = 3;
    } else if (devicePixelRatio >= 2 && (!dpr || dpr >= 2)) {
      dpr = 2;
    } else {
      dpr = 1;
    }
  } else {
    // 其他设备下，仍旧使用1倍的方案
    dpr = 1;
  }
  scale = 1 / dpr;
}

docEl.setAttribute('data-dpr', dpr);
if (!metaEl) {
  metaEl = doc.createElement('meta');
  metaEl.setAttribute('name', 'viewport');
  metaEl.setAttribute('content', 'initial-scale=' + scale + ', maximum-scale=' + scale + ', minimum-scale=' + scale + ', user-scalable=no');
  if (docEl.firstElementChild) {
    docEl.firstElementChild.appendChild(metaEl);
  } else {
    var wrap = doc.createElement('div');
    wrap.appendChild(metaEl);
    doc.write(wrap.innerHTML);
  }
}

function refreshRem() {
  var width = docEl.getBoundingClientRect().width;
  if (width / dpr > 540) {
    width = 540 * dpr;
  }
  var rem = width / 10;
  docEl.style.fontSize = rem + 'px';
  flexible.rem = win.rem = rem;
}

win.addEventListener('resize', function () {
  clearTimeout(tid);
  tid = setTimeout(refreshRem, 300);
}, false);
win.addEventListener('pageshow', function (e) {
  if (e.persisted) {
    clearTimeout(tid);
    tid = setTimeout(refreshRem, 300);
  }
}, false);

refreshRem();

flexible.dpr = win.dpr = dpr;
flexible.refreshRem = refreshRem;
flexible.rem2px = function (d) {
  var val = parseFloat(d) * this.rem;
  if (typeof d === 'string' && d.match(/rem$/)) {
    val += 'px';
  }
  return val;
};
flexible.px2rem = function (d) {
  var val = parseFloat(d) / this.rem;
  if (typeof d === 'string' && d.match(/px$/)) {
    val += 'rem';
  }
  return val;
};
win.dpr = dpr;
win.width = window.document.documentElement.getBoundingClientRect().width;
